Electrolytic cell for production of titanium



G. E. SNOW Aug. 29, 1961 ELECTROLYTIC CELL FOR PRODUCTION OF TITANIUM Filed Feb. 19, 1960 2 Sheets-Sheet 1 FIG. 2

INVENTOR George E. Snow ATTORNEYS G. E. SNOW Aug. 29, 1961 ELECTROLYTIC CELL FOR PRODUCTION OF TITANIUM Filed Feb. 19, 1960 2 Sheets-Sheet 2 FIG.3

INVENTOR George E. Snow BY ATTORNEYS United States Patent 2,998,373 ELECTROLYTIC CELL FOR PRODUCTION OF TITANIUM George E. Snow, Palmerton, Pa, assignor to The New Jersey Zinc Company, New York, N.Y., a corporation of New Jersey Filed Feb. 19, 1960, Ser. No. 9,764 5 Claims. (Cl. 204-246) This invention relates to the production of metallic titanium and, more particularly, to the operation of an electrolytic cell wherein metallic titanium is electro-deposited from a fused salt bath.

In some types of electrolytic operations for the fused salt bath electrodeposition of titanium, it is advantageous or even essential to maintain dilferent bath conditions on opposite sides of the deposition cathode. Such conditions are required in operation of a cell wherein, as described in United States patents to Reimert and Fatzinger No. 2,- 848,397, Andrews No. 2,900,318, Kittleberger No. 2,789,- 943 and Barnett No. 2,908,619, the titanium is deposited on the surface of the cathode distal with respect to the anode. A practical cathode for such an operation comprises a cylindrical structure provided with a bottom wall but open at the top. This permits an anode to be inserted centrally within the confines of the cathode walls. The metallic titanium deposit on the cathode may then be harvested either in situ in the bath or the cathode and anode may be withdrawn from the fused salt bath for harvesting the cathode deposit. A particularly satisfactory form of cathode comprises an open-bottomed cylindrical cathode which, during cell operation, rests upon or adjacent the bottom of the cell in such relation to the cell bottom as to prevent physical contact bet-ween the two portions of the molten bath on opposite sides of the junction of the cathode and the cell bottom. Such a cathode does not require removal of the anode for harvesting of the cathode.

In the course of an electrolysis operation using an open-bottomed cathode, a relatively small amount of metallic titanium tends to deposit adjacent the junction of the lower end of the cathode side walls and the cell bottom. Although this deposition is relatively insignificant at first, it soon becomes suflicient to join the cathode to the cell bottom with such tenacity that the cathode must be pried loose prior to its withdrawal, and upon re turn of the cathode to its operative position the presence of the residual titanium deposit on the bottom of the cell prevents attainment of the desired degree of contact between the bottom of the cathode and the bottom of the cell. Consequently, further deposition of titanium at the junction of the cathode and cell bottom is accelerated, and after a few operating cycles the operation must be discontinued to permit the cell to be drained of salt and the titanium deposit to be removed.

Freezing the fused salt bath electrolyte at the cathodecell bottom junction has been found to be a partial solution to this problem. However, the water cooling necessary to freeze the salt introduces such excessive stresses in the cell bottom as to cause even a metallic cell to crack, and the frozen salt adjacent the cathode bottom requires time for thawing before the cathode is free to be withdrawn.

I have now found that it is possible to construct an open-bottomed cathode in such manner that the deposition of metallic titanium at the junction between the cathode and cell bottom is inhibited so effectively that harvesting of the cathode can be effected repeatedly without suflfering significant deterioration of the desired closeness of contact between the bottom of the cathode side walls and the bottom of the cell. The novel structure of my invention is thus particularly applicable to an electrolytic cell wherein a titaniferous compound in solution in a fused salt bath is electrolyzed using a centrally positioned anode and a surrounding but open-bottomed cathode with deposition of metallic titanium on the distal surface of the cathode. The improved cathode structure of my invention makes it possible to prevent physical contact of anolyte and catholyte portions of the bath on opposite sides of the cathode adjacent this junction and thus prevents deposition of metallic titanium, either electrically or chemically, adjacent the zone of contact or zone of near-contact between the open bottom of the cathode and the bottom of the cell. In addition, the cathode is immediately removable from and easily replaceable in its operative position in the cell. My novel cathode structure comprises an inverted trough-shaped annular chamber connected to the cathode adjacent the open bottom thereof and an upstanding flange on the bottom of the cell extending upwardly into the interior of said chamber. The interior portion of the chamber into which the flange extends is adapted to contain a gaseous atmosphere inert with respect to the fused salt bath, whereby the anolyte and catholyte portions of the bath on opposite sides of the flange are prevented from coming into physical contact with one another by the body of said gas entrapped in the chamber. There is, accordingly, no ionic contact between the anolyte and catholyte adjacent the flange.

These and other novel features of the invention will be readily appreciated upon consideration of the following description of the practice of the invention taken in conjunction With the drawing in which:

FIG. 1 comprises a partial cross-sectional elevation showing the cathode just prior to its ultimate positioning Within the cell;

FIG. 2. is :a partial cross-sectional elevation showing the cathode in its operating position; and

FIG. 3 is a cross-sectional elevation of an electrolytic cell embodying the invention.

In the electrolytic cell 5 shown in FIG. 1, an anode 6 is positioned centrally within the cell. The anode may be suspended above the cell bottom 7 or it may, as in other conventional cell design, extend upwardly through the bottom of the cell. A cylindrically-shaped cathode 8 is concentrically positioned about the anode and divides the molten salt bath within the cell 5 into an anolyte portion A and a catholyte portion C. The lower openbottomed portion of the cathode 8 is. provided with an inwardly (or outwardly) and downwardly projecting flange 10 which, together with the lowermost portion of the cathode, forms an inverted annular trough-shaped chamber around the periphery of the open bottom of the cathode.

As further shown in FIG. 1, the cathode is lowered into its ultimate position only after a gas such as argon, helium, or the like, inert with respect to the fused salt bath, is bubbled intothe inverted trough-shaped chamber through a removable tube 11 or the like. The gas is bubbled into the chamber for a suflicient period of time not only to form a gas pocket in the upper portion of the chamber but to insure complete displacement of air initially trapped in the chamber as the cathode is lowered [from the top of the cell. After this result has been attained, the cathode is lowered to its ultimate position, shown in FIG. 2, with the chamber registering with an upstanding flange 12 struck up from the bottom 7 of the cell. The inert gas trapped in the upper portion of the trough-shaped chamber at the bottom of the cathode prevents the molten salt bath from filling the chamber, and consequently the topof the upstanding flange 12 extends above the level of molten salt within the chamber. This arrangement prevents physical communication between the anolyte and catholyte portions on opposite sides .2 3 of the upstanding flange 12 and thus prevents communication between the main body of anolyte A and catholyte C on opposite sides of the cathode adjacent the bottom of the cathode.

As shown in FIG. 2, the bottom of the cathode 8 can be suspended above and out of contact with the cell bottom 7 in order to maintain electrical isolation of the cathode and cell bottom where this condition is desired. However, the cathode can equally well rest upon the bottom of the cell if this electrical isolation of cathode and cell is not required, and even 'under these conditions it has been found that the lack of physical communication between anolyte and catholyte portions of the fused salt bath prevents the 'formationof any significant amounts of metallic titanium at the zone of contact of the cathode and cell bottom.

The following specific example is illustrative of the use of the novel cathode structure of the invention.

The gas seal device was used in a 72" diameter cell with a 40" diameter bottom entry anode and a 44" diameter cathode operated as described in the United States patent to Reimert and Fatzinger No. 2,848,397. The cathode 8 was supported from the cell roof 13 (FIG. 3) by current-carrying rods 14, and the cell atmosphere above the bath was separated into anode and cathode compartments by a cylindrical baflle 15 in which chlorine evolved from the anode 6 was collected and removed from the cell through an exhaust line 16. The inverted trough-shaped chamber was 4% high with an outside diameter of 48%". The upstanding annular flange 12 attached to the cell bottom was 3% high. Before the start of the run the cathode was lowered almost to the bottom of the cell and argon was introduced into the chamber through a removable pipe with a reverse bend on the bottom. Argon flushing was continued at 2 liters per minute for 20 minutes to insure removal of all entrapped air from the chamber. Then the pipe was removed and the cathode was positioned over the annular flange out of contact with the cell botom. An electrolytic run of 66 hours duration and at 16,000 amperes average current was made pursuant to the aforementioned patent in which 847 liters of TiCls, were reduced to titanium metal. At the end of the run the cathode came ofi the bottom of the cell without difliculty and there was no deposition of titanium in the vicinity of the cathode-cell bottom junction.

I claim:

1. In an electrolytic cell provided with a pervious open-bottomed cathode separating the cell into a catholyte compartment and an anolyte compartment which are in communication with one another only through the porous cathode, a sealing device for joining the cathode to the bottom of the cell which-comprises an inverted troughshaped annular chamber connected to the cathode adjacent the open bottom thereof, and an upstanding flange on the bottom of the cell extending upwardly into the interior of said chamber, the interior portion of the chamber into which the flange extends being adapted to contain a gaseous atmosphere inert with respect to the fused salt bath, whereby the anolyte and catholyte portions of the bath on opposite sides of the flange are prevented from-coming into physical contact with one another by the body of said gas entrapped in the chamber.

2. In an electrolytic cell provided with a pervious open-bottomed cathode separating the cell into a catholyte compartment and an anolyte compartment which are in communication with one another only through the porous cathode, a sealing device for joining the cathode to the bottom of the cell which comprises an inwardly and downwardly extending flange joined to the surf-ace of the cathode above the bottom edge thereof-so as to form an inverted trough-shaped annular chamber connected to the cathode adjacent the open bottom thereof, and an upstanding flange on the bottom of the cell extending upwardly into the interior of said chamber, the interior portion of the chamber into which the flange extends being adapted to contain a gaseous atmosphere inert with respect to the fused salt bath, whereby the anolyte and catholyte portions of the bath on opposite sides of the flange are prevented from coming into physical Contact with one 'ahoth'er by the 'body of said gas entrapped in the chamber.

3. In an electrolytic cell provided with a pervious open-bottomed cathode separating the cell into a catholyte compartment and an anolyte compartment which are in communication withone another only through the porous cathode, a sea-ling device for joining the cathode to the bottom of the cell which comprises an outwardly and downwardly extending flange joined to the 'surfaceof the cathode above the bottom-edge thereof so as to form an inverted trough-shaped annular chamber connected to the cathode adjacent the open bottom thereof, and an upstanding flange on the bottom of the cell extending upwardly into the interior of said chamber, the interior portion of the chamber into which the flange extends being adapted to contain a gaseous atmosphere inert with respect to the fused salt bath, whereby the anolyte and catholyte portions of the bath on opposite sides of the flange are prevented from coming into physical contact with one another by the body of said gas entrapped in the chamber.

4. In an electrolytic cell provided with a pervious open-bottomed cathode separating the cellinto a catholyte compartment and an anolyte compartment which are in communication with'one another only through the porous cathode, a sealing device for joining the cathode to the bottom of the cell which comprises an inverted troughshaped annular chamber connected to the cathode adjacent the open bottom thereof, and an upstanding flange on the bottom of the cell extending upwardly into the interior of said chamber, the interior portion of the chamber into which the flange extends being adapted to contain a gaseous atmosphere inert with respect to the fused salt bath, whereby the anolyte and catholyte portions of the bath on opposite sides of the flange are prevented from coming into physical contact with one another by the body of said gas entrapped in the chamber, the bottom of the cathode being suspended out of physical contact with the cell bottom.

5. In an electrolytic cell provided with a pervious open-bottomed cathode separating the cell into a catholyte compartment and an anolyte compartment which are in communication with one another only through the porous cathode, a sealing device for joining the cathode to the bottom of the cell which comprises an inverted troughshaped annular chamber connected to the cathode adjacent the open bottom thereof, and an upstanding flange on the bottom of the cell extending upwardly into the interior of said chamber, the interior portion of the chamber into which the flange extends being adapted to contain a gaseous atmosphere inert with respect'to the fused salt bath, whereby the anolyte and catholyte portions of the bath on opposite sides of the flange are prevented from coming into physical contact with one another by the body of said gas entrapped in the chamber, the bottom of the cathode being supported on the cell bottom.

References Cited in the file of this patent UNITED STATES PATENTS 2,848,397 Reimert et al. Aug. 19, 1958 2,871,178 Dilling Jan. 27, 1959 2,900,318 Andrews Aug. 18, 1959 2,908,619 Barnett Oct. 13, 1959 

1. IN AN ELECTROLYTIC CELL PROVIDED WITH A PERVIOUS OPEN-BOTTOMED CATHODE SEPARATING THE CELL INTO A CATHOLYTE COMPARTMENT AND AN ANOLYTE COMPARTMENT WHICH ARE IN COMMUNICATION WITH ONE ANOTHER ONLY THROUGH THE POROUS CATHODE, A SEALING DEVICE FOR JOINING THE CATHODE TO THE BOTTOM OF THE CELL WHICH COMPRISES IN INVERTED TROUGHSHAPED ANNULAR CHAMBER CONNECTED TO THE CATHODE ADJACENT THE OPEN BOTTOM THEREOF, AND AN UPSTANDING FLANGE ON THE BOTTOM OF THE CELL EXTENDING UPWARDLY INTO THE INTERIOR OF SAID CHAMBER, THE INTERIOR PORTION OF THE CHAMBER INTO WHICH THE FLANGE EXTENDS BEING ADAPTED TO CONTAIN A GASEOUS ATMOSPHERE INERT WITH RESPECT TO THE FUSED SALT BATH, WHEREBY THE ANOLYTE AND CATHOLYTE PORTIONS OF THE BATH ON OPPOSITE SIDES OF THE FLANGE ARE PREVENTED FROM COMING INTO PHYSICAL CONTACT WITH ONE ANOTHER BY THE BODY OF SAID GAS ENTRAPPED IN THE CHAMBER. 